This invention relates generally to transistor structures, and more particularly the invention relates to a bipolar transistor having a double heterojunction inversion barrier.
Improved speed and transconductance in transistor devices have been achieved by reducing the physical size of the device structures by lithography, processing technology and structural design. However, the decrease in transistor size leads to problems in both junction and MOS transistors, the most serious problem being the punchthrough effect where the collector merges with the emitter of a bipolar transistor or where the drain and source depletion regions begin to merge in MOS transistors.
A new device structure has been proposed by Taylor and Simmons in "The Bipolar Inversion Channel Field Effect Transistor (BICFET)--A New Field Effect Solid State Device: Theory and Structures," IEEE Transactions on Electronic Devices November 1985. This device is bipolar in nature and relies upon the field effect inducement on an inversion layer that corresponds to the conventional neutral base of a bipolar transistor. The device utilizes a heterojunction, and does not have a base layer as in the conventional bipolar transistor. Yokoyama et al. U.S. Pat. No. 4,617,724 also discloses a heterojunction bipolar transistor.